1. Field
The invention is related to ion milling methods and uncooled detectors for imagers which operate in the infrared and far-infrared spectrum. These detectors rely on ferro-electric or pyroelectric materials which become electrically polarized when exposed to infrared radiation.
2. Prior Art
The first pyroelectric imagers were made from thin wafers of very fragile materials with moderate sensitivities in order to utilize phase transitions that occur somewhat near room temperature. Such materials as Tri-Glycine Sulfate (TGS) and Potassium Dihydrogen Phosphate (KDP) are relatively easy to fabricate in the necessarily thin sheets needed to provide rapid response and retard heat dispersion. These materials had transitions temperatures around 300.degree. K. Barium titanate, which is a more durable material, has a much higher value of spontaneous polarization, but is difficult to fabricate and its transition temperature is about 400.degree. K. In the first pyroelectric images detectors these wafers, i.e. TGS and KDP, were incorporated into vacuum tubes known as pyroelectric vidicons and required a coating of silicon oxide to withstand the erosion of an electron beam that scanned it.
Recent work in titanates has produced more rugged fine grain detectors that operate much closer to room temperature. These may be thinned and combined with charge-coupled-devices based on silicon microelectronic technology to produce a more rugged, more sensitive and highly efficient imager. The titanates are initially produced as a fine grain powder precipitated using an alkoxide route. A wafer shaped detector is formed from this powder by high pressure compaction, sintering and thin slicing of the resultant mass with a gem saw. The result is a wafer several mils thick with a rough surface which varies in thickness by at least one micron. To operate properly the wafer must have a surface which retains bulk material properties and a fairly unknown thickness of the order of one micron or less.
Efforts to mechanically grind the above wafer to a thickness of one mil have resulted in surface damage to the molecular structure of the remaining titanates. This is mainly due to a reduction in the oxygen content. To avoid this a liquid etch has been attempted. The etch, however, severely contaminates the wafer, so that even vacuum purging techniques do not remove it. An object of the present invention is, therefore, to provide a detector made from titanates which has the required molecular structure, thickness and surface structure.